Google reviews are easily and frequently manipulated. There are people who sell this as a service using bots and multiple accounts, either hacked or created solely for this purpose. For not much money, certainly far less than a successful scam app might make, you can purchase multiple fake positive reviews, just like you can buy Facebook likes or comments, Twitter likes or comments, forum posts, bumping services, and so on. You shouldn't be trusting Google reviews to tell you what's safe to download.

Don't trust. Verify.